Over heating can be caused by a few things:
1. Incorrect model lamp wattage
2. Poor ventilation by gridded, gelled or confined heads, make sure the head can breathe
3. Exceeding the duty cycle of the flash head
4. A combination of all three.

I am a proponent of cooling fans in heads and following duty cycle recommendations. I have melted a few gels in my day but my Speedo heads are built for high output duty cycles so they just kept on working.